Definition:Odd Integer/Odd-Times Odd
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Definition
Let $n \in \Z$, i.e. let $n$ be an integer.
Definition 1
$n$ is odd-times odd if and only if it is an odd number greater than $1$ which is not prime.
Definition 2
$n$ is odd-times odd if and only if there exist odd numbers $x, y > 1$ such that $n = x y$.
Sequence
The sequence of odd-times odd integers begins:
- $9, 15, 21, 25, 27, \ldots$
Euclid's Definition
In the words of Euclid:
- An odd-times odd number is that which is measured by an odd number according to an odd number.
(The Elements: Book $\text{VII}$: Definition $10$)